The collision of a pair of weather systems right over northeast Illinois has led the National Weather Service to issue an "extraordinarily rare" tornado watch for the area today.

The agency also upgraded the tornado watch to a tornado warning for east central Boone County and northwest McHenry County until 10:15 a.m. That storm is moving northeast at 55 m.p.h. and is over McHenry County. The agency is warning people to "take cover now."

"We're very concerned," weather service meteorologist Gino Izzi said. "We're definitely stressing that this is not your run-of-the-mill tornado watch."

It is in effect for all of the Chicago metropolitan area, including downtown Chicago until 4 p.m., Izzi said. It also extends to all of Illinois, southern Wisconsin and northwest Indiana until 4 p.m.

This is the "top tier"’ of tornado watches that ever gets issued, he said, adding it is "extraordinarily rare."

According to the weather service's Storm Prediction Center in Norman, Okla., "this is a particularly dangerous situation." The center said that several intense tornadoes are "likely," with the possibility of hail up to 2 inches in diameter, and possible wind gusts up to 80 m.p.h.

Beyond the tornado watch, the weather service's outlook for the region includes thunderstorms with occasional wind gusts as high as 75 m.p.h., hail the size of quarters, and the tornadoes, some of which could be "strong and long lived."

The area at risk includes the entire city of Chicago and notably Soldier Field, where the Bears are scheduled to play the Baltimore Ravens at noon, right about the time the storms should be at their worst.

"We've been in contact with the Bears," said Melissa Stratton, a spokeswoman for the Office of Emergency Management and Communications, reading from a prepared statement. "We will continue to monitor the weather and will work with the Bears and Soldier Field (staff) to ensure the safety of the attendees of today's game, should weather become an issue."

Soldier Field has the ability to broadcast messages throughout the stadium and, if necessary, there is shelter for fans inside the stadium. The approach would be to move fans there ahead of time, according to Stratton. OEMC has staff inside the stadium's command center for all major events, she said.

A cold front arriving from the west will collide with the warmer air in Chicagoland to produce the right conditions for storms and tornadoes, meteorologists said, and according to ChicagoWeathercenter.com, the Storm Prediction Center in Norman, Okla., has placed Chicago in an area with high potential for severe weather today.